package library

import (
	"context"
	"errors"
	"fmt"
	"log/slog"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgtype"
	"github.com/jackc/pgx/v5/pgxpool"

	"git.fabledsword.com/bvandeusen/minstrel/internal/coverart"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
	syncpkg "git.fabledsword.com/bvandeusen/minstrel/internal/sync"
)

// Replacing a track with a better copy (M502 #5524).
//
// An upgrade files the better copy first, as a track of its own, and only
// then replaces the old one: its file is removed, then its likes, plays,
// playlist entries and tags move onto the new row and the old row goes. It
// is the duplicate merge with the survivor chosen by the import, and it
// keeps the merge's order (#3918): if the old file cannot be removed nothing
// in the database changes, and the next scan finds the two copies as a
// duplicate pair.

// ErrReplaceSame: the old and new track are one row.
var ErrReplaceSame = errors.New("library: a track cannot replace itself")

// Replaced is what one replacement moved onto the new track.
type Replaced struct {
	PlayEvents      int64
	SkipEvents      int64
	Likes           int
	PlaylistEntries int
}

// ReplaceTrack replaces oldID with newID: the old file is removed, then the
// old row folded into the new one. dataDir, when set, also clears the cached
// art of an artist the fold left with nothing. logger may be nil.
func ReplaceTrack(
	ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger, dataDir string, oldID, newID pgtype.UUID,
) (Replaced, error) {
	if logger == nil {
		logger = slog.Default()
	}
	if oldID == newID {
		return Replaced{}, ErrReplaceSame
	}
	old, err := dbq.New(pool).GetTrackByID(ctx, oldID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return Replaced{}, ErrTrackNotFound
		}
		return Replaced{}, fmt.Errorf("get track: %w", err)
	}
	if err := removeTrackFileOnDisk(old.FilePath); err != nil {
		return Replaced{}, err
	}

	var f foldResult
	err = pgx.BeginFunc(ctx, pool, func(tx pgx.Tx) error {
		changes := mergeChanges{}
		var ferr error
		f, ferr = foldTrackInto(ctx, dbq.New(tx), newID, oldID, &changes)
		if ferr != nil {
			return ferr
		}
		return changes.log(ctx, tx)
	})
	if err != nil {
		return Replaced{}, fmt.Errorf("fold the old track into the new: %w", err)
	}
	if f.DeletedArtistID != nil && dataDir != "" {
		if err := coverart.CleanupArtistArt(dataDir, *f.DeletedArtistID); err != nil {
			logger.Warn("track replace: artist-art cleanup failed",
				"artist_id", syncpkg.FormatUUID(*f.DeletedArtistID), "err", err)
		}
	}
	return Replaced{PlayEvents: f.PlayEvents, SkipEvents: f.SkipEvents, Likes: len(f.Likers),
		PlaylistEntries: f.PlaylistEntries}, nil
}